The invention relates to a hydrostatic clutch actuator for a clutch, particularly a wet-running clutch of a motor vehicle, with the clutch actuator comprising a drive unit, a master-piston cylinder unit driven thereby, a hydraulic reservoir connected in a fluidic fashion to the master-piston cylinder unit, as well as a hydraulic system for the indirect or direct actuation of the clutch, allowing hydraulic medium to be conveyed via the master-piston cylinder unit from the hydraulic reservoir into the hydraulic system and allowing pressure to be applied to the hydraulic system.
Hydraulic clutch actuators are known in prior art which comprise a closed hydraulic reservoir and thus a closed hydraulic system. For the purpose of pressure compensation generally a bellows or a similar pressure compensation unit is provided in the reservoir or in a lid of the reservoir. Such systems of prior art can perhaps have the disadvantage that depending on the geometry of the bellows here pressure compensation is possible to a limited extent only. Furthermore such systems are considered closed systems, however, as shown in the following, under certain circumstances here an increase in the volume of hydraulic substance can occur in the system, which may lead to the actuator failing.
DE 10 2013 204 561 A1 discloses for example a pressure medium-actuating system with an actuator comprising an output element, which is connected via a connection rod to a piston of a piston-cylinder unit. The piston is arranged in an axially displaceable fashion in the cylinder of the piston-cylinder unit such that an operating pressure chamber can vary in its volume so that pressure medium of the operating pressure chamber can be impinged via the connection line in a second operating pressure chamber of a slave cylinder unit, causing the piston in the cylinder of the piston-cylinder unit to be displaced in the axial direction and via a connection rod and a lever or other connection elements, for example, it can actuate a clutch, for example engaging or disengaging it. The piston-cylinder unit is connected via an aperture and a connection line to a pressure medium reservoir. This can be used to connect the operating pressure chamber to the reservoir in a fluidic fashion such that volume compensation can occur.
A hydrostatic actuator arrangement of the applicant, so far not yet published, is known for an actuating device, particularly for a friction clutch device arranged in a drive train of a motor vehicle driven by an internal combustion engine, with the actuator arrangement comprising at least an electric rotary drive with a stator and a rotor, a transmission device for converting a rotary motion into a translational one with at least one ball transmission drive and at least one master cylinder with an axially displaceable piston, with the rotary drive comprising an axis of rotation and the master cylinder comprising a translational axis, and the rotary drive with its axis of rotation and one master cylinder with its translational axis being arranged parallel and at a distance in reference to each other.
From another older application of the applicant, not yet published, either, a hydrostatic system is known comprising a master cylinder with a linearly displaceable master cylinder piston, variably limiting the pressure chamber of the master cylinder, as well as a slave cylinder with a slave cylinder piston limiting a pressure chamber of the slave cylinder, a hydrostatic path filled with pressure medium between the pressure chambers, a compensation vessel filled with a pressure medium, as well as a sensor bore, arranged between the hydrostatic path and the compensation vessel and controlled depending on a position of the master cylinder piston, with a control of the sensor bore being provided outside the pressure chamber.
The three above-mentioned systems exhibit the disadvantage that the hydraulic reservoir is each time embodied in a closed fashion so that pressure compensation must be ensured between the interior of the system and the environment. For this purpose, pressure compensation devices are used, for example in the form of a bellows arranged in the hydraulic reservoir, which generate additional expense and complexity. Another disadvantage of the above-mentioned closed systems is the fact that no exchange and/or no discharge of hydraulic medium out of this system is possible, which can particularly in a hydrostatic clutch actuator for a wet-running clutch can lead to the following problems:
In wet-running clutches any disengagement system (also called CRS) is usually arranged at least partially inside the wet chamber of the clutch. If in the disengagement system a vacuum develops it may occur that via gaskets, sealing the disengagement system in reference to the wet chamber of the clutch, oil can be suctioned into the disengagement system and this way feed it to the hydraulic system between the disengagement system (CRS) and the clutch actuator (HCA). On the long run, an increase of the fill level of the hydraulic system can occur, particularly when the disengagement system regularly and continuously suctions in oil. In case of excessive increase of the fill level and thus the pressure in the hydraulic system it may occur that, due to the extraordinary pressure, with here pressure acting upon the gaskets from the wrong side, namely from the hydraulic to the clutch, gaskets of the disengagement system start leaking and a desired actuation of the clutch becomes impossible.